You get one attack roll for each natural attack you possess, and you do not get any extra natural attack for high BAB (you still gain extra weapon attacks for high BAB if you are using a weapon)
In the case of the Oliphant exposed, because both the Gore and Stamp attacks are primary, you get all the three attacks at your full BAB, and no extra attack because of a high BAB. Assuming your size is Huge:
Melee gore +11 (2d8+5), 2 stamps +11 (2d6+5)
Bonus break down: +8 BAB +5 Str -2 size (because all the three attacks are of primary type, the -5 penalty to secondary attacks does not apply)
The confusion happens because the no BAB extra natural attacks is not clearly stated in the monster rules natural attacks entry, but it is specified in the combat chapter in the natural attacks entry under the Attack section as referenced in the question.
For a full explanation about BAB and natural attacks, first of all, the rule which states you get extra attacks as your Base Bonus Attack (BAB) rises is under common terms definition:
Base Attack Bonus (BAB): Each creature has a base attack bonus and it represents its skill in combat. As a character gains levels or Hit Dice, his base attack bonus improves. When a creature's base attack bonus reaches +6, +11, or +16, he receives an additional attack in combat when he takes a full-attack action (which is one type of full-round action—see Combat).
So by the BAB rule you get additional attacks when you reach certain BAB levels.
Let's check what the natural attacks rules say:
Natural Attacks: Most creatures possess one or more natural attacks (attacks made without a weapon). These attacks fall into one of two categories, primary and secondary attacks. Primary attacks are made using the creature's full base attack bonus and add the creature's full Strength bonus on damage rolls. Secondary attacks are made using the creature's base attack bonus –5 and add only 1/2 the creature's Strength bonus on damage rolls. [...]
Creatures with natural attacks and attacks made with weapons can use both as part of a full attack action (although often a creature must forgo one natural attack for each weapon clutched in that limb, be it a claw, tentacle, or slam). Such creatures attack with their weapons normally but treat all of their natural attacks as secondary attacks during that attack, regardless of the attack's original type.
So nowhere says natural attacks do not get extra attacks for high BAB, but it neither says they do, and it makes a clear difference between natural attacks and attacks made with weapons. So the intention seems clear that natural and weapon attacks are different things and work differently.
The confusion is cleared when you check the natural attacks entry of the Combat section:
You do not receive additional natural attacks for a high base attack bonus.
We can also infer this works like that from examples. In this case take a look to the Bear in Paizo Bestiary. At one side we have the Grizzly Bear (BAB +3) at the other the Dire Bear (BAB +7):
Bear, Grizzly:
Melee 2 claws +7 (1d6+5 plus grab), bite +7 (1d6+5)
Base Atk +3; CMB +9 (+13 grapple); CMD 20 (24 vs. trip)
Bear, Dire:
Melee 2 claws +13 (1d6+7 plus grab), bite +13 (1d8+7)
Base Atk +7; CMB +15 (+19 grapple); CMD 26 (30 vs. trip)
As you can see the Dire Bear has +7 BAB, which corresponds to an attack iteration of +7/+2, but if you look at the Dire Bear attacks, he has exactly the same number and type of attacks than Grizzly bears. Thus, it seems that Pathfinder developers intention is high BAB does not give you access to additional natural attacks, and that is something reserved to weapon attacks, unnarmed strikes and combat maneveurs.
Remember you need to take a full-attack action in order to perform all your natural attacks, and you still benefit from additional attacks if you are holding at least one weapon.
Addendum about natural attack bonuses
When performing multiple natural attacks, you have also to take into account the difference between primary and secondary attacks. So let's see when a natural attack is considered primary or secundary based on the universal monster rules:
Primary: You attack with full BAB and full Strength damage bonus. Are considered primary:
- Typical primary natural attacks: Bite, Claw, Gore, Slam, Sting, Talons
- Whatever attack if it is the only type of natural attack the creature has (be it single attack as a Tile Slap, or multiple as 2 Pincers)
Secondary: You attack with BAB -5 and half Strengh damage bonus. The multiattack feat reduces this penalty from -5 to -2. Are considered secondary:
- Typical secondary natural attacks: Hoof, Tentacle, Wing, Pincers, Tail Slap, Others...
- Whatever attack if it is used in combination with weapon attacks (including unarmed strikes).
A creature that takes a normal full attack action can freely mix melee attacks, ranged attacks, and combat maneuvers counting as attacks
No limitations are placed on what kind of attacks can be made during a full attack, the action specifying only attacks and not requiring, for example, all attacks to be melee attacks because the first attack was a melee attack. (I'm not sure how else such a restriction would be adjudicated—good thing it doesn't matter!) During a full attack combat maneuvers that count as attacks like disarm, sunder, and trip can also be mixed freely alongside those melee and ranged attacks, but combat maneuvers taking a standard action like grapple and overrun can't.
Hence any creature—zen archer monk or not—that takes a full-round action to make a full attack (and not a flurry of blows) can lead with the combat maneuver trip (and possibly provoke attacks of opportunity) then follow that with ranged attacks (and, if threatened, possibly provoke more attacks of opportunity). (Also, such a creature will suffer a −4 penalty on ranged attack rolls made against that prone target.)
The only real advantage a zen archer monk has in using such a tactic is that, due to the monk's extraordinary ability unarmed strike, such a monk really doesn't need to take a free action remove one hand from his bow to attempt the combat maneuver trip then take a free action to put his free hand back on the bow to make the ranged attacks. Whether other creatures attempting the same routine must go through this rigamarole is up to the GM.
Best Answer
Additional attacks made using the full-attack action from a high attack bonus are determined only by your Base Attack Bonus. The rules for Base Attack Bonus say:
Emphasis mine. Your additional attacks are based only on your BAB. No additional bonuses to your attack bonus will change how many attacks you earn for taking a full-attack action.
Therefore, assuming you're making a melee attack:
Note that this does not apply to natural attacks, and that there are other ways to gain additional attacks on a full round attack, such as using two weapons, the spell haste, or the Monk's Flurry of Blows.